1. Field of the Invention
The invention relates to a shift lever position determination device for a vehicle and, more particularly, to an improvement for realizing an accurate position determination that entails no discomfort on a driver's part even in a case where a shift lever-moving operation is stopped without being completed during the use of a majority determination.
2. Description of Related Art
A shift lever position determination device, which determines a shift lever operating position in accordance with a signal from a position sensor, is known. Examples thereof include the shift position determination devices that are disclosed in Japanese Patent Application Publication No. 2013-224693, Japanese Patent Application Publication No. 2008-002561, and Japanese Patent Application Publication No. 2009-216215. According to these techniques, the range of a voltage value corresponding to a specific position and the range of a voltage value corresponding to an adjacent position are defined in advance and, then the shift lever operating position can be determined based on a determination on which of the ranges covers the voltage value of the signal from the position sensor.
The shift lever is selectively operated from an M operating position of mechanical returning in a non-operation state toward any one of an N operating position that is disposed at a position which is adjacent to the M operating position in a select direction, a B operating position that is disposed at a position which is adjacent to the M operating position in a shift direction orthogonal to the select direction, and a D operating position and an R operating position that are disposed at positions which are adjacent to the N operating position on both sides in the shift direction. The shift lever position determination device detects the shift lever operating position based on a comparison between the magnitude of the signal from the position sensor that changes in accordance with the shift lever operating position and a position determination value set in advance.
The position sensor is configured to have a position-fixing circuit board and a magnetic sensor that is fixed to one side of an end portion of the shift lever on the substrate side, detects the intensity of magnetism generated from a magnet fixed to the other side, and outputs a voltage value which continuously changes in accordance with the shift lever operating position. The shift lever operating position is determined based on a result of a comparison between the voltage value and a threshold set in advance. However, the magnitude of the signal from the position sensor varies due to the variations of the characteristics of the magnet mounted on the shift lever, variations of the characteristics of the position sensor, variations of the position of the position sensor fixed to the substrate, and the like. Then, the accuracy of an operating position determination is reduced to cause inconvenience. When the shift lever operating position is positioned in the middle between a predetermined operating position and an operating position that is adjacent thereto, for example, the magnitude of the signal from the position sensor shows the median value of the signals corresponding to the respective operating positions, and thus a value biased toward either one of the operating positions is output due to the above-described variations to cause inconvenience.
In this regard, it is conceivable that predetermined shift lever operating positions are respectively determined in parallel from signals respectively output from a plurality of the position sensors and the operating position is determined based on a majority determination of the determination results. In this case, a highly reliable position determination can be carried out by the majority determination even when any of the position sensors is malfunctioning or abnormal and the shift lever operating position is positioned in the middle between the predetermined operating position and the adjacent operating position.
Still, there is room for improvement with regard to the above-described operating position determination based on the majority determination. In a case where the shift lever operating position is positioned in the middle between the adjacent operating positions as described above, for example, variations of the signals from the position sensors might cause a difference between the operating positions corresponding to the signals from the respective position sensors even when the position sensors are normal. Then, the majority determination as a result might not be satisfied when, for example, the determination result based on two out of four position sensors and the determination result based on the other two of the four position sensors differ from each other.
In the case of a uniform M position determination during the non-satisfaction of the majority determination as described above, the R range is maintained in a case where, for example, the majority determination is not satisfied with the shift lever stopped between the D operating position and the N operating position during the driver's operation of the shift lever from the M operating position toward the D operating position in the R range state. Accordingly, the R range is maintained when the driver is to perform forward traveling based on the satisfaction of the D range through the operation toward the D operating position, and a driving force that is opposite in direction to the driver's intention might be generated. The D range is maintained even in a case where the majority determination is not satisfied with the shift lever stopped between the R operating position and the N operating position during the driver's operation of the shift lever from the M operating position toward the R operating position in the D range state, and thus the D range is maintained when the driver is to perform reverse traveling. Then, a driving force that is opposite in direction to the driver's intention might be generated.
In the case of a uniform N position determination during the non-satisfaction of the majority determination as described above, the operating position is switched to the N range, although the driver is to put engine brake into effect based on the satisfaction of the B range, in a case where, for example, the majority determination is not satisfied with the shift lever stopped between the M operating position and the B operating position during the driver's operation of the shift lever from the M operating position toward the B operating position in the D range state. Accordingly, the engine brake cannot be put into effect as intended by the driver.
In other words, it is impossible to discern whether the shift lever is stopped on the N operating position side or the M operating position side when the majority determination is not satisfied. Accordingly, a uniform N operating position or M operating position determination in this case results in the generation of the opposite driving force due to the R range maintained despite the driver's intention for the forward traveling based on the D range or the unavailability of the engine brake attributable to the switching to the N range despite the driver's intention for the substantial engine brake based on the B range, which, in turn, causes significant inconvenience in the form of discomfort on the driver's part.